1. Field of the Invention
The invention relates to a piston pump for a vehicle brake system, having a housing portion and a piston that is guided displaceably in the housing portion.
2. Description of the Prior Art
The piston pumps used for known vehicle brake systems, particularly anti-lock brake systems (ABS), serve to control the pressure in wheel brake cylinders. In an ABS, the piston pumps are provided for instance for returning brake fluid from one or more wheel brake cylinders to a master cylinder. The ABS often works in combination with traction control (TC). Another known system, the so-called electronic stability program (ESP) improves driving safety by a further increment over ABS and TC. While ABS and TC act in the longitudinal travel direction, ESP affects the crosswise dynamics and therefore in principle is transverse slip control. For all these systems as well as further systems to enhance driving safety, piston pumps are employed.
Known piston pumps intended for vehicle brake systems comprise among other things a cylinder embodied in a housing, in which cylinder a piston is longitudinally movably received. The piston drive is usually effected via an eccentric drive, in which the rotary motion of a shaft, driven by means of a drive motor, is converted into a translational motion of a piston rod of the piston. The piston rod is pressed with its face end against the outer circumference of the eccentric element of the eccentric drive by means of a prestressing element, for instance in the form of a helical spring. Thus in the final analysis, a reciprocating pumping motion of the piston can be achieved.
Known piston pumps for controlling the fluid inflow moreover as a rule have an inlet valve embodied as a seat valve. The inflow of fluid from outside the piston pump to the inlet valve is effected in known piston pumps via a comparatively long suction line, which is embodied in the piston rod and has high flow resistance. As a consequence, known piston pumps used for vehicle brake systems do not have sufficiently effective pressure buildup dynamics, since because of the high flow resistance associated with the very long suction line, they can be filled only relatively slowly. Finally, the production of the piston rods of known piston pumps involves an expensive plunge grinding process.